Dental casting machine



July 6,1926. I 1,591,330 v c. E. LARSON ET AL DENTAL'CASTING MACHINEFiled Jan. 28, 1925 4 Sheets-Sheet 1 3 62 1301:9017 li /21% Ramada/f Bl]ificyi'flffen J July 6 1926. 1,591,330

C. E. LARSON ET AL t DENTAL CASTING MACHINE 4 Sheets-Sheet 2 Filed Jan.28. 1925 i531 Z/lf" flifihaya M Ma,

C. E.- LARSON ET AL July 6, 1926.

DENTAL CASTING MACHINE Filed Jan. 28. 1925 4 Sheets-Sheet 5lmfixzllllllllllllli July 6 1 926.

- 1,591,330 c. E. LARSON El AL DENTAL CASTING MACHINE Filed Jan. 28,1925 4 Sheets-Sheet 4 r-\ I" I Im n 22 45 E Y 4 7' 7/ 7 lg a I1 I z 22-.IE: i 4E: .35

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| v Z3 l l l yjzgy #1617141 Patented m 6, 1926.

UNITED STATES CHARLES E. LARSON AND ERICK ROSEN'DAHL, OI MINNEAPOLIS,MINNESOTA.

DENTAL CASTING MACHINE.

: Application file d January 28, 1925. Serial No. 5,373.

Our present invention relates to machines generally adapted for castingof metal bodies into molds, but, more particularly, to machines forcasting small "articles from the precious metals. More specificallyconsidered, the machine is especially adapted for use in the .dentalprofession to cast in lays, crowns, bridges, and the like, and for thecasting of jewelry. In the casting of dental inlays, for example, greataccuracy and uniformity is required in the molding operation,

It is the general practice to form the molds for dental inlays and thelike in a special investment material of such fine porosity that metalwill not enter the pores thereof but air under pressure will pass quiteslowly through such investment material. In practice, it has been foundthat, by the. use solely of air under pressure, the best castingresultscannot be accomplished because air pockets are liable to be formed inthe mold cavity, and if too great pressure is used or the pressure istoo suddenly applied, the investment material is liable to be fractured.We have found, however, that by subjecting the investing material,during overlapping intervals of time, to the action of partial vacuum,the molten metal toward the bottom of the bowl, and to the action of airunder pressure, tending to force the molten metal down into the mold,substantially perfect inlays or the like may be produced.

For accomplishing the above results, we provide an air compressor,preferably in the form of a cylinder and-piston, and a vacuum-producingdevice, also preferably in the form of a cylinder and piston, and inconnection therewith, provide an operating device, preferably in theform of a lever, by means of which the functions above stated may beproduced.

A commercial form of this improved casting machine is illustrated in theaccompanying drawings, wherein like characters indicate like partsthroughout the several views.-

Referring to the drawingsz' Fig. 1 is a front elevation of the improvedmachine;

' Fig. 2 1s a left side elevation of the machine .Fig. 3 is averticalsection taken on the line 3-3 of Fig. 1; and

Fi 4-. is aview corresponding toFig. 3,

but owing. the machine operative to simu'h tending to drawtaneously'produce air compression and partial vacuum and to render thesame effective on the mold within the flask, as above outlined.

The frame of the machine is preferably a hollow casting involving a base5 and a pedestal 6, the upper end of which latter is forwardly curvedand terminated in a vertical bearing sleeve 7.

v The flask 8, which, as shown is a cylindrical ring, frequentlydesignated as an investment ring, is filled with the investment material9 formed with'a mold cavity 10 and fusing cavity 11, said mold cavityand fusing cavity being connected 0 by a hollow passage, usuallydesignated "as a sprue 12'. In the construction illustrated, the flask 8is seated on a combined cylinder head and flask base 13 that is screwedonto the upper end of a lower cylinder 14;, which, in turn, is bolted orotherwise rigidly secured to the base 5 with its openlower'end alignedwith a clearance passage 15 formed in the latter. As an'importantfeature, the

lower end of the flask 8 is directly seated on' a packing ring 16,preferably of braided in the customary way steam packing tightly pressedinto a dovetailed annular groove formed in thehead 13. Preferably also,the head 13 is formed with several of the dove-tailed annular groovesfilled with packing material and arranged, one packing ring for eachsize of flask to be used. The head 13 has an upstanding annular flangewithin which is,

seated a centering ring 17 that fits closely around the flask or ring 8and properly centers the same. For each flask ofvarying diameter therewould be rovided a spacing ring 17 fitting around the same by fittingwithin the flange of the head 13.

One or more, preferably several, small air ports 18 are formed in thehead 13 to connect the upper end of the cylinder 14 to the lower innerportion of the flask 8. Working within the cylinder 14 is a piston 19,the stem of which depends through the clearance passage 15 and, asshown, is connected to one end .of-a" lever 20, the other endof which ispivoted at 21 to a lug on the in- Y terior of the base 5. 1 Aswillpresently appear, the cylinder 14 and piston 19 'consti-' tute thevacuum-producing device, that is, the device for producing partialvacuum.

Working vertically through the bearing sleeve 7 in axial alignmentwiththe cylinder. 14 and flask 8, is aplunger 22, the lower end of whichis rigidly secured to the head 23 of an upper cylinder 24. Workingwithin the cylinder .24 is a piston 25, which, as shown,

has a depending tubular stem 26 to which stem 26 and is provided at itsupper end with one or more, preferably several, small air ports 29. Theupper end of the thimble 28 terminates above a leather packing disk 30carried by the top of the piston 25. The piston 25 is normally held atthe lower end of the cylinder 24 and against stop screws 31, partly bythe action of gravity and partly by the action of a coiled spring 32.

The flask cover 27, preferably and as shown, is made as an elementseparable from the piston 25 and it is provided with concentric packingrings 33 set into annular dove-tailed grooves and .corresponding intheir diameter and general purpose to the packing rings 16, beforedescribed, except that the said packing rings 33 are engageable with theupper ends of-the flask to form air-tight joints therewith. One or more,preferably several, small air ports 34 are formed in the central portionof the cover 27 and are arranged to deliver air under compression fromthe cylinder 24 to the upper portion of the flask in the castingoperation hereinafter described.

. For holding the plunger 22 and the parts carried thereby in depressedpositions for reasons that will fully appear in the description of theoperation, there is provided 'a pawl and ratchet latch. This latch, asshown, comprises a ratchet-toothed steel bar 22 set into and rigidlysecured to the plunger 22, and a spring-pressed latch dog 35 pivoted tothe sleeve 7 with its beveled-end working through a notch in the latterand engageablewith the teeth of the bar 22.

The operating device shown is in the form of a lever 36 pivotallyconnected at one end to the upper ends of a pair of links 37, extendedone on each side of the pedestal 6 and at their lower ends pivotallyanchored thereto at 38. r

The intermediate portion of the lever 36 is connected to the plunger 22,and this may be done in different ways but, preferably, it isaccomplished through laterally spaced links 39. These links 39, at-theirlower ends, are pivoted on a nut-equipped bolt 40 that is passed throughthe hub of the cylinder head 23 and the'lower end of, the plunger 22 4and performs the additional function of se-. curing said cylinder headto said plunger. The upper, ends of the links 39 are, secured by nuts orotherwise to the ends of a cross rod 42. The u per end of the plunger 22is bifurcated so t at it embraces the lever 36. The lever 36 is pivotedon the central portion of the cross rod 42 and said cross rod is passedwith a large amount of clearance through holes 43 formed in the prongsat the upper end of the plunger 22. With this arrangement, the lever 36does not directly act upon the plunger 22 but indirectly acts thereonthrough the links 39 and applies its downward pressure thereto at thelower end of said plunger and at a point below the bearing sleeve 7.

The lever 36 has a connection for operating the piston 19 through thelever 20. This connection performs not only the major function indicatedbut also highly important minor functions and, as designed to carry outall of these functions, comprises as follows: a connecting link made upof three main elements 44, 45 and 46. The element 44 is a screw-threadedrod, which, at its lower end, works through a .passage in the top of thebase 5 and is pivotally connected to the intermediate portion of thelever 20.

The upper end of the rod 44 is screwed into the lowerv end of theintermediate section 45 and is adjustably secured by a lock nut47. Theupper section 46 is telescoped into an axial bore 45 formed in the upperportion of the section 45, so that said section 46 acts as a'plunger.The upper end of the plunger 46 is bifurcated so that it embraces thelever 36 and its bifurcated end is provided with a sort of wrist pin 48that is engageable with any one of several notches 49 formed in theupper side of the long slot 50 provided in said lever adjacent to itspivoted end. 4 leaf spring 51 is secured to the lever 36 and follows theslot 50, so that it yieldingly holds the wrist pin 48 engaged with thenotch 49 in which it is positioned. By a slight depression of the spring51, the wrist pin 49 may be readily shifted into engagement with any oneof the connected to the cylinder 24, and the numeral 55 indicates avacuum gauge that is connected to the cylinder 14.

Operation.

The operation of this machine for is substantially as follows:

1 Normally, the parts all stand asshown in Fig. 3. The metal, by meansof a blowpipe or otherwise, will be melted within the fusing cavity 11,but under the action of gravity, no part of this molten metal will runcasting course,

of the flask 8, the plunger 46 will strike the bottom of the bowl 45 andthereby cause plied to the top of the entire link'44-4546 to movedownwvard as a unit and thereby impart a downward movement to the piston19. This initial downward movement of the piston 19 will produce apartial vacuum in the upper portion of the cylinder 14 and, hence,commence the downward drawing action on the molten metal before the airpressure is apthe flask, and this draws from the flask certain gases aswell as the air from the mold 10. Immediately following this initialsuction or partial vacuumproducing action, the flask cover 27, undercontinued downward movement of the lever 36, will tightly seal-itselfagainst the top of the flask, thereby stopping further downward movementof the piston 25, so that continued downward movement of the cylinder 24will produce air pressure which will be delivered through the tubularstem 26 and ports 34 directly against the upper portion of theinvestment material 9 and against the.

upper portion of the molten metal in the fusing cavity 11. It will thusbe seen that the action of partial vacuum and air pressure are thenbrought into action on the investment material and the molten metal, theformer tending to suck or draw the molten metal down into the mold andthe latter tending. to ress the same downward into the mold. The extentto which'the above actions will take place will be regulated by theextent to which the lever '36 is forced downward. The operator watchingthe gauges .54 and 55 can readily determine when the proper pressure andvacuum have been produced, and will then stop further pressure on thelever, at which point the dog 35, engaging the ratchet bar 22, will lockthe plunger 22, cylinder 24 and flask cover 27 in their loweredoperative positions shown in Fig. 4. The above action does not produce asudden shock. or high pressure within the flask, but there will be acomparatively slow but continued flow of "the compressed air from thecylinder 24 downward through the investment material until the pressuresin the pressure cylinder 24 and vaciium cylinder-14 have been equalized.During the time that the equalization 'of pressure 15 taking place, themetal will be forced into the: mold, caused toa completely fill the moldand to solidify The before the cover 27 engages the top suctionaction'produced by the artial vacuum removes the gases and air rom theinvestment material and mold and effectually eliminates all air pocketsand resulting flaws in the casting, and for'that reason, as we havefound in practice, it is advisable to render the partial vacuum orsuction action slightly in advance of the delivery of compressed aironto the molten metal. Of course, the time interval between the twoactions noted is very short and, moreover. it

may be'varied by adjustments of the link sections 44 and 45, the .one inrespect to the other. By the latch dog 34, the depressed elements may beheld down as long as desired and until it is certain that the castinghas properly crystallized or set. If, at

any time during the setting operation above described, thegauges shouldindicate a drop in the air pressure, additional pressure may beinstantly a plied by giving the lever 36 a slightly fart er downwardmovement.

Preferably, the spring 52 is of such tension that it will hold thepiston 19 raised at any time the machine is not in use and, in fact,would hold said piston against downward movement even if an adjustmentshould be made wherein the air pressure was delivered to the flask inadvance of the partial vacuum and until the lever 20 .is given apositive downward movement through the mechanical connections described.It is further highly important to note that, in this machine, thevacuum-producing device made up of the cylinder 14 and piston 19, islocated immediately below and, adjacent to the flask and that, in thenormal position of the parts, there is practically no air-containingspace between'the piston 19 and the flask and from this, it follows thatthe initial downward movement of the piston 19 will instantly produce orstart suction or partial vacuum in the flask,

and from this, it also follows that very slight movement of the piston19 is required to produce the desired partial vacuum or suction. It isfurther important to note that this machine,'by the manipulation of asimple operating device or lever, is caused to produce its own airpressure and partial vacuum. Otherwise stated, this machine is aself-contained machine that requires no connections to or associationwith an air storage tank or other source of air supply. Moreover, themachine is capable of being easily manipulated to any desired pressure.A person using the machine will soon be able to predetermine or knowapproximately the pressure that will be required to best produce'anypardesired pressures have been produced.

' A's already indicated, adjustments of the l n se tion 44; and 45 w ldetermine the accurately produce v ticular kind of casting and thegauges ill indicate when such predetermined or iae relative times ofbringing the vacuum-producing and air-compressing devices into action,and-it has also-been noted thatthe said air-compressing andvacuum-producing devices will be continued in action during overlappingintervalsof time, and during which time the casting will be formed andcaused to crystallize or set.- The amount oi vacuum that will beproduced for a predetermined down 'ard movement of the lever oroperating device 36 may be varied by adjustments of the wrist pin 48 inthe notches 49 of the lever 36, and it may be further stated that thecloser the pin 48 is set to the pivot 37, the less will be the partialvacuum produced and, conversely, the farther the pin 48 is set from thepivot 37, the greater will be the partial vacuum produced. Of course,adjustments of the pivotal. connection between the plunger 46 and thelever 36 will require re-adjustments of the sections 44 and 4:") to setthe vacuumproducing! and air-compressing devices, the former for actionin advance of the latter. It will be noted that in this machine, the aircompressor afforded by the described cylinder and piston is a completeor-selfcontained expansible and contractible air compressor having itsown and enclosed air- 9 containing chamber. Moreover, it will be notedthat this air compressor is located immediately above the flask, so thatthe heat applied to melt the metal in the mold will rise and preheat theair in the said cham- 3 ber. This preheating ot' the air is importantbecause, when the air-compressing action takes place, hot dry air willbe forced against the metal in the mold.

WVhat we claim is:

' 1. A casting machine comprising a 001m 1 plete or self-contained aircompressor and a vacuum producer in opposing arrangement and adapted toengage and close an interposed flask containing an investment materialin which a mold .is formed and an operating device having a connectionfor throwing said air compressor and vacuum producer into action duringoverlapping intervals of time.

9 f 2. A casting machine comprising a complete or self-contained aircompressor and a" vacuum producer in opposing arrangement and adapted toengage and close an interposed flask containing an investment materialin which a mold is. formed, and an operating device having a connectionfor throwing said air compressor and vacuum producer into action duringoverlapping intervals of time, but with the action of the latter startedahead of the former.

-3. The structure defined in claim 1 in further combination with a latchoperative to hold said air compressor. and vacuum producer set forpredetermined actions.

A, The structure definedii n claim 2 in further combination with a latchoperative to hold said air compressor and vacuum producer set forpredetermined actions.

5. A casting machine comprising a flask for containing the investmentmaterial in '(0 which a mold is formed, an expansible and contractiblepressure-producing device and a vacuum-producing device, the former ar--ranged to deliver compressed air to said flask and the latter arrangedfor drawing air from said flask, and an operating device havingconnections for operating said two devices with an overlapping intervalof action, whereby metal in the flask will be simultaneously subjectedto air pressure on one side and to vacuum on the other side.

6. A'casting machine comprising a flask for containing the investmentmaterial in which a mold is formed, a pressure-producing devicecomprising a cylinder and piston, a vacuum-producing device comprising acylinder and piston, the piston of said pressure-producing device havinga flask cover and an air port for delivering air pressure into theflask,and the cylinder of said vacmun-producing device having a portionaffording a flask base and provided with an air port for drawing airfrom the flask, and an operating device having connections for movingthe cylinder of said pressure-producing device and the piston of saidvacuum-producing device, whereby the metal' in said mold will, during anoverlappng interval, be subjected to air pressure on one side and vacuumon the other side.

7. The structure defined in claim 5 in further combination with meansfor throwing said pressureproducing device and vacuum-producing deviceinto action and for setting the same in action, the one underpredetermined air pressure and the other under predetermined vacuumpressure.

8. A casting machine comprising means for supporting a flask that isopen at both ends and contains a porous mold-forming investmentmaterial, a complete self-contained air compressor and'a vacuum provducer in opposing arrangement and adapted to engage and close theopposite ends of said flask, and means for operating said air/compressor and vacuum producer and for renderng the same active on theinvestment material in said flask during overlapping intervals of time.

9. In a casting machine, a supportingframe, a vacuum-producing cylinderand piston, the former being anchored to the base of said frame andprovided witha head aflording a flaskbase, a flaskseated on said baseandcontaining. an investment material I in which a mold is formed, saidcylinder head having a port connecting, said cylinder to the lowerportion of said flask, a plunger mounted to move through the upperportion'ot said, frame imsubstantial align-- 39 with duce a compressionof an on said ment with said lower cylinder, a pressureproducingcylinder and piston, the former being secured zto the .lower end. ofsaid plunger and the latter having a fiaskcover and a port fordelivering air from said latter noted cylinder into the, upper portionof'said flask, and a lever'having connections for moving said lower'iston, to produce or moving said cylinder and piston, to proto bedelivered flask cover is seated plunger, upper into said flask when saidflask. 10. The structure defined in claim 9 in combination with meansfor-latching said plunger, upper c linder and piston in a depressedposition to therebymaintain the 'air pressure in the upper cylinder andthe artialvacuum in the lower cylinder dur- 1ng an overlapping intervalof time. 11. The structure defined in claim 1 in which said operatingconnection is adjustable to vary the relative tension of throw-j ingsaid air compressor and vacuum producer into action.

12. The structure defined in claim in 'which said operating connectionis ad ust ably attached to said operating device for varying the extentof partial vacuum produced b said vacuum producer.

13. The structure defined in claim 1 in which saidoperating connectionincludes a lever and several telescoped elements, one of whichtelescoped elements ing movement, theother part of said connection beingspring-retracted.

14. In a casting machine, the combination a frame including a base andpedestal, of a. vacuum-producing device comprising a and the latterhaving an has a limited slidcylinder and piston, the former beingsecured to said base and, having a hea affording a flask-supportingbase, said head havlng an air passage, a lever connected to said baseand to said piston, .a plunger working through thejupper portion of saidedestal substantially in axial alignment with said cylinder, an aircompresn com prising a c linder and piston, the former beingsecure tothe lower end of said plunger I air discharge pas sage and a'flaskcover, an operating'lever connected to said pedestal and plunger andoperative tovertically move said' plunger and parts carried thereby,necting said operating lever to said'lower lever forv operating thepiston of said vacuum device.

15. The structure defined in claim 14 in which said plunger is providedwith ratchet teeth, and in further combination with a latch dog mountedon the upper portion of said pedestal and 1vot. In testimony whereof weaflix our signatures. I I

- CHARLES E. LARSON.

. ERICK ROSENDAHL;

and a link con-- operative on said ratchet teeth to hold said aircompressor and be ore it is a from the lever

